1. Field of the Invention
The present invention relates to a TTL-ECL converting circuit, and more specifically to a TTL-ECL converting circuit which operates at a high speed and which is free from self-oscillation.
2. Description of Related Art
Recently, ECL (emitter coupled logic) circuits in the form of an integrated circuit having a high integration density have been used in various fields requiring a high speed operation, for example, so-called main frames, communication instruments, LSI testers, measuring instruments, etc. In many cases, however, the above mentioned instruments are provided, as a memory, with an inexpensive standard semiconductor memory having a TTL (transistor-transistor logic) interface. Therefore, an interface of the ECL integrated circuit having a high integration density has been provided with a TTL-ECL level converting circuit, and therefore, both an ECL interface and a TTL interface have been assembled within a single LSI chip.
However, the conventional TTL-ECL level converting circuits have been disadvantageous in that a base potential of a transistor receiving a TTL input signal is apt to cause vibration, and the vibrating voltage is propagated as noises to an ECL level output signal. The noise has the possibility of causing a next stage of ECL circuit to malfunction.
Furthermore, the conventional TTL-ECL level converting circuits have a logical amplitude of the ECL output signal much larger than the logical amplitude in ordinary ECL circuits. Therefore, the propagation delay time is inevitably large.